• Rubn (13/13) Apr 24 2018 I was wondering if I could create my own property in a way that
• Jonathan M Davis (10/23) Apr 24 2018 If you're dealing with a user-defined type, you can declare an enum or
• Meta (21/34) Apr 24 2018 If you don't control T and can't add members, then the best thing

Rubn <where is.this> writes:

I was wondering if I could create my own property in a way that 
can be used the same way as something like "T.sizeof". Right now 
I have the following to replace length:

uint length32(T)(T[] array)
{
     return cast(uint)array.length;
}

I want something similar to be able to do the following:


uint size = T.sizeof32;

The closest I can think of is doing:

uint size = sizeof32!T


That's the best I can do, which is fine but I was wondering if 
there's any other way around that?

Jonathan M Davis <newsgroup.d jmdavisprog.com> writes:

On Tuesday, April 24, 2018 21:36:19 Rubn via Digitalmars-d-learn wrote:
 I was wondering if I could create my own property in a way that
 can be used the same way as something like "T.sizeof". Right now
 I have the following to replace length:

 uint length32(T)(T[] array)
 {
      return cast(uint)array.length;
 }

 I want something similar to be able to do the following:


 uint size = T.sizeof32;

 The closest I can think of is doing:

 uint size = sizeof32!T


 That's the best I can do, which is fine but I was wondering if
 there's any other way around that?

If you're dealing with a user-defined type, you can declare an enum or
static function on it to do something like T.sizeof32. However, you can't
add stuff like that without editing the type itself, so it won't work with
any types that you aren't defining yourself - especially built-in types.

If you're willing to use an instance of the type, then you can declare a
free function and use UFCS, but as soon as you want to use the type itself,
you're going to need to use a template, which means something like
sizeof32!T rather than T.sizeof32.

- Jonathan M Davis

Meta <jared771 gmail.com> writes:

On Tuesday, 24 April 2018 at 21:36:19 UTC, Rubn wrote:
 I was wondering if I could create my own property in a way that 
 can be used the same way as something like "T.sizeof". Right 
 now I have the following to replace length:

 uint length32(T)(T[] array)
 {
     return cast(uint)array.length;
 }

 I want something similar to be able to do the following:


 uint size = T.sizeof32;

 The closest I can think of is doing:

 uint size = sizeof32!T


 That's the best I can do, which is fine but I was wondering if 
 there's any other way around that?

If you don't control T and can't add members, then the best thing 
you can probably do is instead write T.init.sizeof32. Actually, 
though, you can be sneaky about it and use a local function to 
shadow Test, but this is probably more trouble than it's worth:

import std.stdio;

struct Test
{
}

 property sizeof32(Test t) { return 1; }

void main()
{
      property Test() { return .Test.init; }
     writeln(Test.sizeof32);
}

This is really annoying, though, because you have to declare the 
Test function in every function or struct/class definition you 
use it in. You can create a mixin that does it automatically, but 
you'd still have to do `mixin(testProperties)` (where 
testProperties is an enum you've defined that's just the function 
definition).